There is always a need to develop biodegradable lubricants for use in applications which might result in the leakage of such lubricants into the soil and into waterways, such as rivers, oceans and lakes. Base stocks for biodegradable lubricant applications such as two-cycle engine oils, catapult oils, hydraulic fluids, drilling fluids, water turbine oils, greases, gear lubricants, shock absorber fluids, plasticizers, internal lubricants, and the like have to meet increasingly stringent criteria such as enhanced biodegradability, higher viscosity index, better lubricity, better demulsibility, better additive solubility, lower density, etc. than existing lubricants.
One class of compounds that have the potential of meeting the above requirements are complex esters which are polyol esters of dicarboxylic acids and polyols, especially trifunctional polyols. Examples of such polyols are described in U.S. Pat. No. 5,912,214, the entire contents of which are incorporated herein by reference.
However, it has been found that complex polyol esters which contain short chain dicarboxylic acid residues, such as adipic acid, often exhibit diminished biodegradability, demulsibility, lubricity and additive solubility in the higher viscosity (higher average molecular weight) versions. It has also been observed that complex polyol esters which contain longer chain dicarboxylic acid residues such as “dimer” acid (C36-54 difunctional) often exhibit diminished biodegradability and demulsibility in the higher viscosity (higher average molecular weight) versions.